[time-nuts] Fundamental limits on performance

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Sun Sep 13 16:23:06 UTC 2009

On 9/13/09 5:02 AM, "Magnus Danielson" <magnus at rubidium.dyndns.org> wrote:

> I doubt it. Looks like another antenna and set of receiver electronics.
> Unless someone does something smart, it looks like it can be ruled out
> from power and weigth constraints. Pulsars are there thought and if
> several can be observed their beat frequency would be fairly low such
> that phase-relationships can act like a positioning in space and time.
> It may be good to have redundancy such that gravitational potential can
> be resolved separately.
> Space-ship to space-ship or earth station needs to rely on the link
> between them. Synchronous carrier helps alot and stable clocks in each
> end require less dynamics for steering.

The way we do this now is to lock the local reference oscillator (on the
spacecraft) to the uplink signal, which is derived from a Hydrogen Maser.
But that requires that the uplink be there, and there's really only about
half a dozen places in the world that can radiate the signal, and there are
multiple other consumers of the resource.

Starting with a good quality clock helps (after all, no amount of fancy
control system can stiffen a wet noodle)

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